JPS61216718A - Wet waste gas desulfurization apparatus - Google Patents

Abstract

PURPOSE:To reduce the volumes of the machinery and piping valves of a slurry system, by providing a classifier to the line discharging a slurry to the next process or to the outside of the system from the recirculation tank of an absorbing tower and selectively separating gypsum from the slurry to recover the same to an absorbing system as a seed crystal. CONSTITUTION:SOX in exhaust gas is absorbed and removed by a slurry containing a Ca absorbent in an absorbing tower 3. Gypsum particles are selectively concn. and separated in the cyclone 17 provided to the line for withdrawing a part of the recirculation slurry to a reaction tank 10 from the recirculation tank 5 of the absorbing tower 3 and a proper amount of the gypsum concn. slurry is supplied to the recirculation tank 5 of the absorbing tower 3 through a conduit 18 so that the concn. of gypsum in the absorbent slurry in the recirculation tank 5 of the absorbing tower 3 is set to predetermined concn. to be recovered as a seed crystal.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a wet flue gas desulfurization system, and particularly relates to a wet flue gas desulfurization system that collects seed crystals to prevent scaling of an absorption system. be.

(Prior Art) The mainstream wet flue gas desulfurization equipment currently in practical use uses a calcium-based absorbent and recovers gypsum as a by-product. That is, the limestone-gypsum method (or lime-gypsum method) uses limestone, quicklime or slaked lime as an absorbent.

FIG. 5 is an explanatory diagram of a conventional flue gas desulfurization device that uses limestone as an absorbent and recovers gypsum as a byproduct. Exhaust gas 1 from a boiler or the like is led to a dust tower 2, where it is cooled and dust removed, and then led to an absorption tower 3, where it comes into contact with circulating slurry, and after the mist is removed by a demister 4, Absorption tower 3
is discharged from the top. On the other hand, limestone slurry, which is an absorbent slurry, is supplied to the absorption tower circulation tank 5 by a limestone slurry pump 9, and the slurry is supplied to a spray nozzle 8 installed in the absorption tower by an absorption tower circulation pump 7, and comes into contact with the exhaust gas. Then, it absorbs and removes SOx in the exhaust gas, returns to the circulation tank, and is used for circulation. After absorption, the slurry is extracted to a by-product recovery system.

By adding sulfuric acid to the slurry taken out to the reaction tank 10, unreacted limestone is converted into gypsum, and the slurry is adjusted to p) which is suitable for oxidation.

The pH-adjusted slurry is supplied to the oxidation tower 12 by the oxidation tower supply pump 11, where the calcium sulfite is air oxidized to become gypsum, and is led to the thickener 13'.
After being concentrated, the gypsum slurry is hydrophilized in a centrifuge 14 and powdered gypsum 15 is recovered. The overflow water of Shisofuna is reused as make-up water within the system.

On the other hand, in order to prevent scaling of the absorption system, a certain amount of the gypsum waste slurry from the shisofuna is supplied into the centrifuge waste liquid tank 14 through the conduit 16 so that the gypsum concentration in the absorption tower circulation tank 5 is 5 wt% or more, and seed crystals are As absorption tower circulation tank 5
is returning to .

(Problems to be Solved by the Invention) However, in such a conventional device, the slurry from Shisofuna 13, which has the highest slurry concentration in the system (approximately 20 wt%
Since the slurry (slurry) is collected as seed crystals, the amount of slurry is circulated from the absorption system to the gypsum recovery system in an amount equal to the amount of seed crystals, and all equipment (tanks, pumps) and piping valves must be enlarged. Furthermore, as the size of the pumps increases, the motor output increases, resulting in increased power consumption. For the above reasons, there has been a demand for a desulfurization device that reduces equipment, piping valves, and utilities.

An object of the present invention is to provide a wet flue gas desulfurization device that eliminates the drawbacks of the prior art described above and reduces the capacity of slurry-based equipment and pipe valves that make up the majority of the desulfurization device.

(Means for Solving the Problems) In short, the present invention focuses on the fact that the particle size of gypsum (CaSO4.2H20) produced by the reaction between SOx and the absorbent is the largest among the solids in the absorbent slurry. Then, a device for separating gypsum particles, such as a cyclone, multi-cyclone, or thickener, is installed in the line that extracts the slurry from the absorption tower circulation tank, and gypsum is selectively separated and concentrated from the absorption slurry, and this is used as seed crystals. This is how it was done.

That is, the present invention allows sulfur dioxide gas in the exhaust gas to be brought into contact with calcium-based absorbent slurry circulated from the absorption tower circulation tank within the absorption tower, and then supplied to the next process for gypsum recovery. , or in wet flue gas desulfurization equipment that discharges gypsum as it is without recovering it, a classifier is installed in the slurry line that discharges the slurry from the absorption tower circulation tank to the next process or outside the system, and separates the gypsum from the solids in the slurry. It is characterized by the provision of a line for selectively separating and recovering a certain amount of it as a seed crystal into an absorption system.

In the present invention, if gypsum is not to be recovered as a by-product, a classifier may be installed in the line that discharges the slurry from the absorbent slurry circulation tank (or its circulation line), and if gypsum is to be recovered, the absorbent A classifier may be provided in the line that supplies slurry from the tower circulation tank (or its circulation line) to the reaction tank (or oxidation tower) in the next step.

Examples of the classifier include a cyclone, a multi-cyclone, and a thickener, but the classifier is not limited to the above as long as it can selectively collect gypsum particles. When a multi-cyclone is set, the recovery amount can be controlled by operating the multi-cyclone according to the change in content.

(Example) An example of the present invention will be described below with reference to FIG. This device is the same as the conventional device shown in Figure 5 except for the absorbent slurry circulation system in the absorption tower, but a part of the circulating slurry in the absorption tower circulation tank 5 is extracted and used as a gypsum pre-separation device in a cyclone. The difference is that after the particles are concentrated and separated, a conduit 18 is provided to draw out an appropriate amount of the gypsum concentrated slurry so that the gypsum concentration in the absorbent slurry in the absorption tower circulation tank 5 reaches a predetermined concentration. That is, exhaust gas 1 from a boiler or the like is led to a dust removal tower 2, where it is removed and cooled, and then introduced into an absorption tower 3. Here, SOx in the exhaust gas is removed by a slurry containing a calcium-based absorbent, and then
The entrained mist is removed by the demisf 4 and discharged from the absorption tower. On the other hand, the absorbent slurry is supplied to an absorption tower circulation tank 5, and then supplied to the absorption tower by an absorption tower circulation pump 7 for circulation use. A portion of the slurry in the absorption tower circulation tank 5 is extracted to the reaction tank 1-0 in proportion to the amount of absorbent slurry supplied. The solids in this slurry include calcium sulfite produced by the reaction between the absorbent and SOx, unreacted absorbent, dust in the gas, impurities in the absorbent, and the reaction between oxygen in the gas and calcium sulfite. This is the gypsum produced. These reaction formulas are as follows.

CaCO3+SO2+H20− Ca SO3□ ], / 2 H20+ C○2+
1/2H20Ca SO3' 1/2H20+1/20
2 +3/2H20Ca SO4□ 2 H20 In the present invention, as shown in Table 1, gypsum (CaSO3.2H20) particles are the largest among the solids in the slurry, so this gypsum is selectively removed by the cyclone 17. The gypsum is concentrated and separated, and the amount necessary for the gypsum concentration in the absorption system slurry to reach a predetermined concentration (5 wt% or more) is collected as seed crystals into the absorption tower circulation tank 5 via the conduit 18.

Table 1 Meanwhile, the slurry after separating the seed crystals is extracted through a conduit 19 to a conventional by-product recovery system (reaction tank 10 or below).

Using the cyclone shown in FIG. 4 as the cyclone 17, solid-liquid separation was performed at a flow rate of 5 m/5eC5 slurry concentration of 10.1 wt% in the slurry input port 20, and the particle size in the liquid in the slurry outlet port 21 was 30 μm or less. It became.

On the other hand, the concentrated slurry containing gypsum particles of 30 μm or more is taken out from the seed crystal recovery port 22 and returned to the absorption tower circulation tank 6. In this way, calcium sulfite of 30 μm or less, unreacted absorbent, dust in the gas, and impurities in the absorbent are separated from the gypsum and supplied to the byproduct recovery system, and the gypsum is separated from these. It can be collected as seed crystals.

Next, FIG. 2 shows another embodiment of the present invention, in which a multi-cyclone 17A is provided instead of a cyclone in order to cope with load changes and intermediate load operation.
The amount of seed crystals recovered is controlled by controlling the extraction amount with the flow rate controller 24 and the control valve 16 in accordance with the amount of Ox, and controlling the processing quantity of the multi-cyclone with the 0N-OFF valve 23 in accordance with the extraction amount. It was designed to do so.

In this way, by controlling the amount of seed crystals collected from the conduit 18A in response to load changes, smooth operation of the apparatus can be achieved.

Further, FIG. 3 shows a case where the slurry is discarded after collecting the seed crystals with the classifier 17 in the case where by-product recovery equipment is not installed after the absorption system.

Although the above embodiments have all been described with respect to a dust separation system as a desulfurization system, the present invention can be similarly applied to a dust mixing system.

(Effects of the Invention) According to the present invention, in order to recover seed crystals between the slurry after absorption and the reaction tank after being extracted to the by-product recovery system, the equipment and piping valves of the by-product recovery system without making it larger than necessary, i.e. by the amount of recovered seed crystals (for example, about 10%)
) The capacity of equipment and piping valves can be reduced,
Furthermore, by making the equipment smaller, it is also possible to reduce power consumption. Further, if a by-product recovery system is not provided, seed crystals cannot be recovered in the steps after the oxidation step, so the present invention is particularly effective.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the flow of the wet flue gas desulfurization apparatus according to the present invention, Fig. 2 is a diagram showing an embodiment in which a multi-cyclone is adopted as the classifier of the present invention, and Fig. Figure 4 is a front view of the cyclone used in the present invention, and Figure 5 is a conventional wet flue gas desulfurization device. FIG.

Claims (3)

[Claims] (1) After the sulfur dioxide gas in the flue gas comes into contact with the calcium-based absorbent slurry circulated from the absorption tower circulation tank in the absorption tower, it is either supplied to the next process for gypsum recovery, or the gypsum is recovered. In wet flue gas desulfurization equipment that discharges the slurry as is without removing it, a classifier is installed in the slurry line that discharges the slurry from the absorption tower circulation tank to the next process or outside the system, and selectively separates gypsum from the solids in the slurry. A wet flue gas desulfurization device is characterized in that it is equipped with a line that collects a certain amount of it into an absorption system as a seed crystal. (2) The wet flue gas desulfurization apparatus according to claim 1, characterized in that a cyclone or a thickener is installed as a classifier. (3) The wet flue gas desulfurization device according to claim 1, characterized in that a multi-cyclone is installed as a classifier, and the amount of recovery can be controlled according to the load when the load changes.